D1 Dopamine receptor-mediated substance P depletion in the striatonigral neurons of rats subjected to neonatal dopaminergic denervation: implications for self-injurious behavior

The present study examined the influences of dopamine (DA) receptor stimulation on enkephalin (Met5-enkephalin; ME) and tachykinin (substance P; SP) systems of basal ganglia of Sprague-Dawley rats, lesioned as neonates with 6-hydroxydopamine (6-OHDA). It has been proposed that the neonatal 6-OHDA-lesioned rat could serve as a model for the DA deficiency and self-injurious behavior (SIB) observed in the childhood neurological disorder. Lesch-Nyhan syndrome. In agreement with earlier work, the present study found that the neonatal 6-OHDA treatment at 3 days of age, reduced DA and caused an increase in ME and a decrease in SP content in the striatum and substantia nigra, when tested as adults. Administration of the DA precursor, L-dihydroxyphenylalanine (L-DOPA), to lesioned animals, induced SIB; increased DA and DOPAC levels; produced a greater decrease (-64%) in SP levels in the striatum and substantia nigra than was observed with lesion alone (-28%). The L-DOPA-induced decrease in SP levels and the SIB observed in the lesioned animals were blocked by pretreatment with the D1 receptor antagonist, SCH-23390. Moreover, administration of the D1 receptor agonist, SKF-38393, but not the D2 agonist, LY-171555, to lesioned animals mimicked the L-DOPA responses in all respects, except that the agonists did not alter DA or DOPAC levels. None of the DA agonists or antagonists treatments affected lesion-induced increase in ME levels in the striatum. These results indicate for the first time, that SIB precipitated by DA agonists in neonatal dopaminergic denervated animals, is associated with a marked and selective decrease in SP in the striatonigral SP neurons. This process has two components: (a) a retarded development of the SP system due to neonatal dopaminergic denervation: and (b) a depletion of the remaining SP, presumably by enhanced release due to D1 DA receptor-mediated activation of striatonigral SP neurons.     

Enhanced stimulus-reward learning by intra-amygdala administration of a D3 dopamine receptor agonist

The amygdala is considered to be a critical neural substrate underlying the formation of stimulus-reward associations, and is known to receive substantial innervation from dopaminergic neurons located within the ventral mesencephalon. However, relat- ively little is known about the function of the mesoamygdaloid dopamine projection in stimulus-reward learning. Recently, we have found post-session intra-amygdala microinjections of d-amphetamine to enhance appetitive Pavlovian conditioning as assessed in a discriminative approach task. In the present study, we have examined the effects of dopamine receptor agonists possessing relative selectivity for the D₁, D₂ and D₃ receptor subtypes in order to examine more fully the role of the mesoamygdaloid dopamine projection in stimulus-reward learning. Thus, subjects were trained to associate an initially neutral stimulus (CS⁺) with 10% sucrose reward (US). A second, control stimulus (CS⁻) was also presented but never paired with sucrose reward. In order to measure specifically the conditioned response to CS⁺/CS⁻ presentation, responding during CS and US presentations was measured separately. Immediately following each training session, subjects received bilateral intra-amygdala infusion of 0.1, 1 or 10 nmol/side of SKF-38393, quinpirole or 7-OH-DPAT. Infusions of SKF-38393 or quinpirole were without effect on CS⁺ approach. However, post-session intra-amygdala infusions of 7-OH-DPAT enhanced selectively CS⁺ approach in a dose-dependent fashion. No dose of any drug affected CS⁻approach, US behaviours, or measures of extraneous behaviour. Subsequent acquisition of a novel conditioned instrumental response was also unaffected. Thus, the present data indicate a selective involvement of the D₃ dopamine receptor subtype in the modulation of stimulus-reward learning by the mesoamygdaloid dopamine projection. Received: 12 December 1996 / Final version: 9 April 1997     

Dopamine receptor agonists alter gap prestimulus modulation

An innocuous sensory event (a prestimulus) that briefly precedes a startle-eliciting stimulus (SES) will reduce the amplitude of the subsequently elicited reflex. In three experiments brief silent periods in otherwise continuous noise (gaps) were used as prestimuli to investigate the effects of the D₁ dopamine receptor agonist (±)-SKF-38393 (SKF) and the dopamine D₂ receptor group agonist (−)-quinpirole hydrochloride on gap inhibition of the rat’s acoustic startle reflex. Gap durations of 4 and 50 ms were analyzed. Quinpirole (0–1.6 mg/kg) had a biphasic effect on gap inhibition. Lower doses increased gap inhibition, an effect that peaked at the 0.4 mg/kg dose. For higher doses, inhibition returned to control levels for the 4-ms long gap, but remained elevated for the 50-ms long gap. SKF had no effect on gap inhibition, and haloperidol (0.2 mg/kg) reversed the quinpirole-induced increase of gap inhibition. These data implicate the D₂ dopamine receptor group in gap inhibition of startle modulation. The results are discussed in terms of the effects of catecholamine agonists on attention. Received: 25 July 1995/Final version: 28 April 1997     

Neurophysiological investigation of effects of the D-1 agonist SKF 38393 on tonic activity of substantia nigra dopamine neurons

The effects of the D-1 agonist SKF 38393 on tonic activity of rat substantia nigra pars compacta dopamine neurons were studied using extracellular, single-unit recording techniques. Unlike nonselective D-1/D-2 dopamine agonists or the D-2 agonist quinpirole, SKF 38393 did not inhibit dopamine neuronal activity when applied iontophoretically or when administered intravenously in doses up to 20 mg/kg to chloral hydrate-anesthetized rats. Moreover, pretreatment with SKF 38393 did not alter the inhibitory response of these neurons to apomorphine or the D-2 agonist quinpirole. However, in locally anesthetized, gallamine-treated, artificially respired rats, dopamine cell activity was significantly altered by i.v. administration of SKF 38393; firing rate increases and decreases were observed. Administration of the inactive enantiomer of SKF 38393, S-SKF 38393, did not induce similar changes in parallel experiments. These results support the idea that unlike D-2 autoreceptor stimulation, D-1 receptor stimulation does not exert a direct local effect on dopamine neurons in the substantia nigra pars compacta and suggest that D-1 receptor stimulation at sites postsynaptic to the dopamine cells may indirectly affect the activity of some dopamine neurons through long-loop feedback mechanisms.     

Modulation of MK-801 response by dopaminergic agents in mice

Various doses of the non-competitive N-methyl-d-aspartate (NMDA) receptor antagonists, MK-801 (0.1–0.5 mg/kg) and ketamine (2.5–10 mg/kg), produced a dose-dependent increase in stereotypic behaviour in naive mice. MK-801 (0.1 mg/kg) and ketamine (2.5 mg/kg) potentiated the stereotypic response of apomorphine (0.1–0.5 mg/kg) in mice pretreated with reserpine (5 mg/kg, 24 h prior) and alpha-methyl-p-tyrosine (150 mg/kg, 1 h prior) but not in naive mice. SKF 38393, a D₁ dopamine agonist, enhanced whereas B-HT 920, a D₂ dopamine agonist, reduced the stereotypic response of MK-801 in naive mice. The response of MK-801 was blocked by pretreatment with haloperidol (0.5 mg/kg), molindone (2.5 mg/kg), clozapine (7.5 mg/kg) and SCH 23390 (0.1 mg/kg). The present data suggest involvement of endogenous DA transmission in the stimulant action of non-competitive NMDA antagonists in mice. Dopamine D₁ and D₂ receptor stimulation, respectively, exert opposing effects on the behavioural expression of MK-801 in mice.     

Behavioral effects of dopaminergic agonists and antagonists alone and in combination in the squirrel monkey

The effects on schedule-controlled operant behavior of the D₂ receptor agonist, quinpirole, and the D₁ agonist, SKF 38393, were assessed alone and in combination with selective dopamine-receptor antagonists. Squirrel monkeys (Saimiri sciureus) were trained to press a response key under fixed-interval and fixed-ratio schedules of food reinforcement. The fixed-interval schedule maintained relatively low rates of responding that increased up to food presentation. The fixed-ratio schedule maintained relatively constant high rates of responding. Quinpirole increased rates and disrupted the temporal pattern of responding under the fixed-interval schedule at doses (0.1–1.0 mg/kg) that decreased rates of responding under the fixed-ratio schedule. Under the fixed-interval schedule, the D₂ antagonists, spiperone (0.003–0.006 mg/kg) and haloperidol (0.003–0.01 mg/kg), and the D₁ antagonist, SCH 23390 (0.03 mg/kg), shifted the quinpirole dose-effect curve to the right. The maximal effects of quinpirole were decreased at the highest doses of the antagonists. However, only spiperone antagonized effects of quinpirole on the rates of responding under the fixed-ratio schedule. The D₁ agonist, SKF 38393, dose-dependently (1.0–10.0 mg/kg) decreased rates of responding under both schedules. Those effects were not antagonized by any doses studied of either spiperone (0.003 mg/kg) or SCH 23390 (0.003–0.3 mg/kg). Rather, both antagonists enhanced the effects of SKF 38393. The present study suggests significant differences between the effects of D₁ and D₂ agonists on schedule-controlled behavior, and differences in the antagonist actions of the D₂ antagonists haloperidol and spiperone. Further, the selective dopamine D₁ agonist, SKF 38393, has behavioral effects that cannot be antagonized by either a D₁ or D₂ antagonist, suggesting that some other mechanism has a significant role in mediating its behavioral effects.     

Chronic treatment with MK-801 affects the behavioral response to both D1 and D2 dopamine agonist in the one-trial inhibitory avoidance

Post-training administration of theN-methyl-d-aspartate (NMDA) antagonists CPP (0.5 and 1.0 mg/kg) and MK-801 (0.25 and 0.5 mg/kg) impaired, in a dose dependent fashion, the one-trial inhibitory avoidance response in NMRI mice. The D₁ dopamine (DA) agonist SKF 38393 (10 and 20 mg/kg) and the D₂ agonist quinpirole (0.5 and 1.0 mg/kg) instead facilitate the response in the same behavioral paradigm. Sub-chronic blockade of NMDA receptors with MK-801 (0.25 mg/kg once a day for 14 days) did not change the response to both competitive (CPP) and non-competitive (MK-801) NMDA antagonists. The same chronic treatment with MK-801 induced an increased response to both SKF 38393 and quinpirole. These data suggest that repeated administration of MK-801 induce an upregulation of both D₁ and D₂ DA receptors without affecting NMDA receptors.     

Selective attenuation of the antinociceptive effects of μ opioids by the putative dopamine D3 agonist 7-OH-DPAT

Rationale: The purpose of the present investigation was to evaluate the effects of the D₃ agonist (±)-7-hydroxy-dipropylaminotetralin (7-OH-DPAT), various dopamine (DA) agonists and DA antagonists on the antinociceptive effects of μ opioids. Methods: Antinociception was assessed using a warm-water tail-withdrawal procedure in rats. Results: The μ opioids morphine (0.3–10 mg/kg) and dezocine (0.03–3.0 mg/kg) produced dose-dependent increases in antinociception with maximal effects obtained at the higher doses tested. Pretreatment with the putative D₃ agonist 7-OH-DPAT (1.0–10 mg/kg) produced a dose-dependent attenuation of the antinociceptive effects of morphine and dezocine. At the highest dose of 7-OH-DPAT tested, the morphine dose-effect curve was shifted rightward by approximately 1.5 log units and the dezocine curve by greater than 2.3 log units. The (+)-isomer of 7-OH-DPAT (1.0 and 3.0 mg/kg) also shifted the morphine dose-effect curve to the right in a dose-dependent manner. The DA D₃/D₂ agonist (−)-quinpirole (0.1–10 mg/kg) attenuated the effects of morphine, but these effects were small in magnitude, not dose-dependent and observed only under a limited set of conditions. The DA D₂/D₃ antagonist spiperone failed to alter the morphine dose-effect curve, but reversed the effects of 7-OH-DPAT on morphine antinociception. Pretreatment with the DA D₁ agonist (±)-SKF38393 (1.0 and 10 mg/kg) and the D₁ antagonist (+)-SCH23390 (0.1 and 1.0 mg/kg) failed to alter the morphine dose-effect curve. Conclusion: The finding that 7-OH-DPAT markedly attenuated the effects of morphine and that these effects were reversed with spiperone suggests that activity at the D₃, and possibly the D₂, receptor can modulate μ agonist-induced antinociception. Received: 30 June 1998/Final version: 12 January 1999     

Dopamine D1 receptor activation induces dehydroepiandrosterone sulfotransferase （SULT2A1） in HepG2 cells

Aim： Dopamine receptors are present in the nervous system and also widely distributed in the periphery. The aim of this study was to investigate the role of D1 subtype dopamine receptors （DRD1） in the regulation of dehydroepiandrosterone sulfotransferase （SULT2A1） in HepG2 cells. Methods： HepG2 cells were treated with DRD1 agonists with or without DRD1 antagonist for 9 d. DRD1 and SULT2A1 mRNA expression, protein expression, and SULT2A1 activity were detected using RT-PCR, Western blotting and HPLC, respectively. The level of cAMP was measured using a commercial kit. Results： All the 5 DR subtypes （DRD1-DRD1） were found to be expressed in HepG2 cells. Treatment of HepG2 cells with the specific DRD1 agonists SKF82958 （2.5 μmol/L） or SKF38393 （5 and 50 μmol/L） significantly increased the mRNA and protein expression of both DRD1 and SULT2A1, and increased SULT2A1 activity and cAMP levels. These effects were partially blocked by co-treatment with the specific DRD1 antagonist SCH23390 （2.5 μmol/L）. In addition, transfection of HepG2 cells with DRD1-specific siRNAs decreased DRD1 mRNA expression by 40%, which resulted in the reduction of SULT2A1 mRNA expression by 60%, protein expression by 40%, and enzyme activity by 20%. Conclusion： DRD1 activation upregulates DRD1 and SULT2A1 expression and SULT2A1 activity in HepG2 cells, suggesting that the DRD1 subtype may be involved in the metabolism of drugs and xenobiotics through regulating SULT2A1.     

钙池操纵性钙通道抑制剂SKF96365对慢性哮喘小鼠气道重塑和气道高反应性的作用

目的:观察钙池操纵性钙通道抑制剂SKF96365对小鼠慢性哮喘模型气道重塑和气道高反应性的影响。方法:用鸡卵清白蛋白(OVA)致敏和激发小鼠,建立慢性哮喘模型,33只雌性BALB/c小鼠随机分为3组:对照组、哮喘组、SKF96365组,每组11只,其中SKF96365组于每次激发前30 min给予SKF96365(10mg/kg)干预。哮喘组和SKF96365组于第0、7、14 d腹腔注射(i.p)200μL致敏液(含OVA粉剂20μg、氢氧化铝凝胶2 mg);自第21天起,腹腔注射1%戊巴比妥钠(70mg戊巴比妥钠/kg小鼠体重)麻醉小鼠后,OVA(40μg)滴鼻(i.n),连续6周,每周3次,共18次。对照组则在相同时间给予相应剂量的生理盐水腹腔注射和滴鼻。最后一次激发后24 h,各组分别随机取5只小鼠用于检测组织病理学变化,另6只小鼠采用Buxco小动物肺功能仪检测气道高反应性。其中组织病理学检测计算杯状细胞(过碘酸希夫染色阳性,PAS+)、胶原细胞(Masson阳性)和平滑肌细胞(α-SMA阳性)阳染面积/支气管基底膜周长值来评估小鼠气道重塑;观察给予不同浓度乙酰甲胆碱雾化时的气道阻力(resistance index,RI)最大值,评估小鼠气道高反应性。结果:对照组未见PAS阳性染色区域,哮喘组和SKF96365组杯状细胞增生高于对照组(7.29±2.04,4.49±1.70 vs 0.00±0.00,均P0.01),且SKF96365组低于哮喘组(P0.05)。Masson染色显示哮喘组和SKF96365组上皮下胶原沉积高于对照组(9.23±1.41,7.30±1.33 vs 1.60±0.77,均P0.01),且SKF96365组低于哮喘组(P0.05)。α-SMA免疫组化显示哮喘组和SKF96365组平滑肌增生肥大高于对照组(4.54±1.05,3.15±0.57 vs 1.97±0.69,均P0.05),且SKF96365组低于哮喘组(P0.05)。当乙酰甲胆碱(Mch)≤6.25 mg/m L时,3组小鼠气道阻力无显著差异(P0.05),当25 mg/m LMch≥12.25 mg/m L时,哮喘组小鼠气道阻力明显大于对照组小鼠(P0.001),当Mch≥25 mg/m L时,哮喘组小鼠气道阻力大于SKF96365组(P0.05)。结论:采用SKF96365干预后,慢性哮喘小鼠气道重塑和气道高反应性指标均有改善,提示SKF96365可能对哮喘气道重塑和气道高反应性具有抑制作用。